1. Field
The present invention relates to a packet forwarding apparatus, and a controlling method.
2. Description of the Related Art
Conventionally, a packet forwarding apparatus handling an Ethernet (registered trademark) packet represented by an L2 switch or an L2 router is required to provide a warranty called QoS (Quality of Service).
Specifically, the packet forwarding apparatus performs a congestion control by a burst resistance and priority processing by using a packet buffer in a network of a 1:1 or N:1 connection. For example, the packet forwarding apparatus, equipped with a packet buffer for storing a received packet, identifies a priority (class) of the received packet and stores it into the packet buffer according to the priority (class). The packet forwarding apparatus transmits the packet of a higher priority (class) in preference and transmits the packet of a lower priority (class) over a residual band left by transmitting the packet of the higher priority (class) (generally called a best effort).
The packet forwarding apparatus stores the packet of the higher priority in preference in the packet buffer. For this reason, at the time of storing the received packet in the packet buffer, when the packet buffer has little space for storage, the packet forwarding apparatus discards the packet of the lower priority without storing it in the packet buffer.
Various technologies have been developed for such QoS. For example, Japanese Patent Application Laid-open Publication No. 2005-12431 (pages 1 to 5, FIG. 1) discloses the technology of impartially distributing the packet buffer set for the best effort for a plurality of flows. Namely, the packet forwarding apparatus according to Japanese Patent Application Laid-open Publication No. 2005-12431 stores the packets in excess of a band warranty in the packet buffer set for the best effort. Here, in the case of existence of a plurality of flows, the packet forwarding apparatus according to Japanese Patent Application Laid-open Publication No. 2005-12431 impartially distributes capacity of queue for the best effort among the plurality of flows, irrespective of magnitude of respective data volumes of the plurality of flows and stores the packets.
For example, Japanese Patent Application Laid-open Publication No. 2005-244417 (pages 1 and 5 (in particular, paragraph numbers [0026], etc.), FIG. 4) discloses the technology of assigning the band assigned for the band warranty to the band for the best effort, using the token. Namely, the packet forwarding apparatus of Japanese Patent Application Laid-open No. 2005-244417 monitors an unspent token volume at each point in time and determines whether there is any unspent token at the time of adding a next token to a token packet and if it is determined that the unspent token is left, assigns the band assigned for the band warranty to the band for the best effort, using the token.
Incidentally, the above conventional technologies had the problem of not being capable of decreasing opportunity of discarded packets while using the buffer efficiently or of maintaining the band control based on the class (packet transmission processing by the priority control based on the class).